The present invention relates to a method and apparatus for detecting a defect in a surface of a substrate and, more particularly, to a substrate surface inspecting method and apparatus suitable for detecting a linear defect in a surface of a magnetic disk substrate.
For an apparatus for inspecting a surface of a substrate for a magnetic disk, there is a need to classify detected defects in order to contribute to sophistication in process management and improvement in process. Generally, a detection optical system in an apparatus for inspecting a surface of a substrate for a magnetic disk includes plural detectors. In addition to classification of micro defects by detection signals from the plural detectors, classification of the defects on the basis of a feature to a distribution shape of the defects in a magnetic disk face is requested. Specifically, although continuous micro defects can be recognized as linear defects, defects distributed discretely and linearly (hereinbelow, written as a linear scratch defect) have to be discriminated from a collection of the other micro defects.
For example, Japanese Patent Application Laid-Open Publication No. 2000-180376 (patent document 1) discloses an apparatus for detecting a defect in a surface of a magnetic disk, which emits a laser beam to a magnetic disk as a sample to be inspected, receiving reflection light and scattering light from the surface of the magnetic disk by plural detectors, and classifying micro defects in accordance with light reception conditions of light receivers of the detectors. By determining continuity in a plane of the detected micro defects, the length of the defect is detected and, the defects are classified to a linear defect and a lump defect.
Japanese Patent Application Laid-Open Publication No. 2009-180590 (patent document 2) describes that, using an apparatus for detecting a defect in a surface of a magnetic disk similar to that described in the patent document 1, the cycles of linear defects are detected to detect a wrinkled defect.
Further, Japanese Patent Application Laid-Open Publication No. 2006-352173 (patent document 3) describes a technique of classifying defects in accordance with a state of a distribution of defects obtained by testing the surface of a semiconductor wafer.
Defects linearly distributed include continuously linear defects and defects which are discretely distributed in a linear region. In the defect classifying method described in the patent document 1, although continuously linear defects can be detected as linear defects, detection of defects which are discretely distributed in a linear region (continuous scratch defect) so as to be discriminated from random micro defects is not considered. In the invention disclosed in the patent document 2, since increase/decrease in reflection light generated by mild roughness in the surface of a magnetic disk is detected, micro defects cannot be detected. Further, in the defect classifying method described in the patent document 3, only the defect position information is used. Consequently, it is difficult to select and process a defect point having a specific feature from defects obtained from the plural detectors.